Transcript How Evolution Works

How Evolution Works
Genes, Geography and Sex
Early Idea: Lamarckian
Evolution
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Fossil record
indicated increasing
complexity
Reasoned traits are
passed via use and
disuse
e.g. the giraffe’s
neck
Step 1: Raw Material
Genes are raw material
 Forms of genes = alleles
 Polygenic vs. Single gene trait
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Selection on a Single Gene:
The Peppered Moth
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Before Industrial
Revolution
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After Industrial
Revolution
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Single gene
controlling a trait
will have only a few
(usually 2 or 3
phenotypes)
Variation and Selection
Variation from two sources
1) New mutations = new allele types
2) Gene shuffling = new allele
combinations
 Any change in allele frequency =
Evolution
 Peppered Moth Simulation
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Polygenic Traits
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More than one gene controls a trait
Selection and Changing the
Norm
Most traits are polygenic
 The normal trait is the average or
mean in the population
 Selection changes the mean, usually
lowers variation
 Selection will adjust mean
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Stabilizing Selection
Disruptive Selection
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Can lead to new species
Does Evolution Ever Stop?
YES, but only if the following conditions
are met
1) Random mating
2) Large Population
3) No movement in or out of
population
4) No Mutations
5) No Natural Selection
 Hardy Weinberg Equilibrium
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How New Species Are Formed
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Two populations must become
reproductively isolated
Behavioral Isolation

Groups differ in mating, feeding,
sleep/awake cycles so members of
populations do not meet to mate
Rana aurora (Redlegged frog)
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Breeds in fast moving
streams
Rana catesbiana
(Common bullfrog)
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Breeds in still ponds
Geographic Isolation
Geological Time and Evolution
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First fossils 3.5 bya
Stromalites
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550 mya =
Cambrian Explosion
(by fossil evidence)
Dating Fossil Age
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Relative Dating
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Radioisotope Dating
Known decay times
of isotopes can be
used
Extinction and Adaptive
Radiation
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Most species cannot
adapt
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Those that can
radiate into open
niches
Evolution Patterns
Convergent Evolution
Coevolution